Piezoelectric actuator and method for manufacturing piezoelectric actuator

ABSTRACT

A piezoelectric actuator includes a substrate, a first electrode arranged on the substrate, a piezoelectric body stacked on the first electrode, a second electrode superimposed on a surface of the piezoelectric body on a side opposite to the first electrode, and a wiring connected to the first electrode. The first electrode has a connecting portion which is arranged to protrude from an end portion of the piezoelectric body and to which the wiring is connected, and a first conductive portion is provided so that the first conductive portion overlaps with the first electrode while extending over from an area overlapped with the end portion of the piezoelectric body up to the connecting portion of the first electrode.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. patent applicationSer. No. 14/844,233 filed on Sep. 3, 2015, which claims priority fromJapanese Patent Application No. 2014-197243 filed on Sep. 26, 2014, thedisclosures of which are incorporated herein by reference in theirentirety.

BACKGROUND Field of the Invention

The present teaching relates to a piezoelectric actuator and a methodfor manufacturing the piezoelectric actuator.

Description of the Related Art

Japanese Patent Application Laid-open No. 2013-111819 discloses apiezoelectric actuator which is provided to discharge the ink fromnozzles of a recording head based on the ink-jet system. Thepiezoelectric actuator is arranged on a flow passage forming substratecomposed of silicon which is formed with a plurality of pressurechambers. Note that the plurality of pressure chambers are communicatedrespectively with the plurality of nozzles of a nozzle plate joined tothe flow passage forming substrate.

The piezoelectric actuator is provided with a plurality of piezoelectricelements which correspond to the plurality of pressure chambersrespectively. The plurality of piezoelectric elements is arrangedopposingly to the plurality of pressure chambers respectively on anelastic film of the flow passage forming substrate which covers theplurality of pressure chambers. Each of the piezoelectric elements has alower electrode film, a piezoelectric body, and an upper electrode filmwhich are stacked in this order from the side of the flow passageforming substrate. The lower electrode film is an individual electrodewhich is provided individually for each of the piezoelectric bodies. Awiring (lead electrode) is connected to a portion of the lower electrodefilm which is exposed while protruding from the piezoelectric body. Onthe other hand, the upper electrode films are in conduction with eachother among the plurality of piezoelectric elements, and the upperelectrode film functions as a common electrode. When a voltage isapplied between the lower electrode film and the upper electrode film ineach of the piezoelectric elements, then the deformation occurs in thepiezoelectric body, and thus the pressure of the ink contained in thepressure chamber is raised. Accordingly, the ink is discharged from thenozzle which is communicated with the pressure chamber.

The piezoelectric actuator described above is manufactured by performingthe following steps. At first, an electrode film is formed as a film onthe elastic film of the flow passage forming substrate, for example, bymeans of the sputtering method. The patterning is performed for theelectrode film to form the plurality of lower electrode films.Subsequently, a piezoelectric material film is formed as a film on thesubstantially entire surface of the elastic film formed with theplurality of lower electrode films. After that, the piezoelectricmaterial film is subjected to the patterning to form the plurality ofpiezoelectric bodies which cover the plurality of lower electrode filmsrespectively. Subsequently, an electrode film is formed as a film tocover the plurality of piezoelectric bodies, and then the electrode filmis subjected to the patterning to form the upper electrode film.

SUMMARY

As described above, the piezoelectric material film is formed as thefilm on the entire surface of the elastic film, and then unnecessaryportions of the piezoelectric material film are removed by means of theetching to perform the patterning in the piezoelectric body forming stepincluded in the manufacturing of the piezoelectric actuator. However, itis feared that a part of the lower electrode film, which is arranged onthe lower side of the piezoelectric material film, may be removedtogether when the etching is performed for the piezoelectric materialfilm. In particular, if the portion of the lower electrode film, whichis to be connected to the wiring (lead electrode), is scraped off, thereliability of the electric connection is lowered between the lowerelectrode film and the wiring.

An object of the present teaching is to avoid the deterioration of thereliability of the electric connection between an electrode and a wiringon account of the simultaneous removal of the electrode disposed on thelower side when a piezoelectric body is formed by means of thepatterning.

According to a first aspect of the present teaching, there is provided apiezoelectric actuator including a substrate; a first electrode arrangedon the substrate; a piezoelectric body stacked on the first electrode; asecond electrode superimposed on a surface of the piezoelectric body ona side opposite to the first electrode; and a wiring connected to thefirst electrode, wherein the first electrode has a connecting portionwhich is arranged to protrude from an end portion of the piezoelectricbody and to which the wiring is connected, and a first conductiveportion is provided so that the first conductive portion overlaps withthe first electrode while extending over from an area overlapped withthe end portion of the piezoelectric body up to the connecting portionof the first electrode.

In the present teaching, the first conductive portion overlaps with thefirst electrode so that the first conductive portion extends over fromthe area of the first electrode overlapped with the end portion of thepiezoelectric body to the connecting portion protruding from the endportion of the piezoelectric body. Note that the first conductiveportion may be arranged on the upper side of the first electrode, or thefirst conductive portion may be arranged on the lower side of the firstelectrode. When the first conductive portion covers the first electrode,the simultaneous removal of the first electrode is suppressed by thefirst conductive portion during the etching for the piezoelectricmaterial film when the piezoelectric body is formed. On the other hand,when the first conductive portion is disposed on the lower side of thefirst electrode, the electrical connection is maintained between theconnecting portion of the first electrode and the wiring, even when apart of the first electrode is removed during the etching for thepiezoelectric material film, because the first conductive portion stillexists thereunder.

According to a second aspect of the present teaching, there is provideda piezoelectric actuator including a substrate; a first electrodearranged on the substrate; a piezoelectric body stacked on the firstelectrode; a second electrode superimposed on a surface of thepiezoelectric body on a side opposite to the first electrode; and awiring connected to the first electrode, wherein a first conductiveportion is provided so that the first conductive portion overlaps withthe first electrode in an area overlapped with an end portion of thepiezoelectric body, and at least one of the first electrode and thefirst conductive portion has a connecting portion which protrudes fromthe end portion of the piezoelectric body and to which the wiring isconnected.

In the present teaching, the first electrode and the first conductiveportion are arranged in an overlapped manner in the area overlapped withthe end portion of the piezoelectric body. Therefore, even if the upperlayer portion of the first electrode and the first conductive portion isremoved during the etching for the piezoelectric material film when thepiezoelectric body is formed, then the lower layer portion remains, andthus the electrical connection is maintained between the first electrodeand the wiring.

According to a third aspect of the present teaching, there is provided amethod for manufacturing a piezoelectric actuator provided with asubstrate, a first electrode arranged on the substrate, a piezoelectricbody stacked on the first electrode, a second electrode superimposed ona surface of the piezoelectric body on a side opposite to the firstelectrode, and a wiring connected to the first electrode, the methodincluding: a first electrode forming step of forming the first electrodeon the substrate; a first conductive portion forming step of forming afirst conductive portion which overlaps with the first electrode whileextending over from an area of the first electrode in which thepiezoelectric body is arranged up to a connecting portion which isconnected to the wiring; a piezoelectric film forming step of forming apiezoelectric material film so that the first electrode is coveredtherewith, after the first electrode forming step and the firstconductive portion forming step; a piezoelectric film patterning step offorming the piezoelectric body by performing patterning for thepiezoelectric material film by means of etching and removing a portionof the piezoelectric material film which covers the connecting portionof the first electrode; and a wiring forming step of forming the wiringto be connected to the connecting portion of the first electrode afterthe piezoelectric film patterning step.

The first conductive portion is superimposed on the first electrode,while extending over from the connecting portion to the portion of thefirst electrode at which the piezoelectric body is arranged. Therefore,in a case that the first conductive portion covers the first electrode,the first electrode is prevented from being removed together when theetching is performed for the piezoelectric material film. Further, in acase that the first conductive portion is disposed on the lower side ofthe first electrode, even if a part of the first electrode is removedduring the etching for the piezoelectric material film, then theelectrical connection is maintained between the connecting portion ofthe first electrode and the wiring, because the first conductive portionstill exists thereunder.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view illustrating a printer according to thisembodiment.

FIG. 2 is a top view illustrating one head unit of an ink-jet head.

FIG. 3 is an enlarged view illustrating a portion A in FIG. 2.

FIG. 4 is a sectional view taken along a line IV-IV in FIG. 3.

FIG. 5 is a sectional view taken along a line V-V in FIG. 3.

FIG. 6A depicts a vibration film forming step, FIG. 6B depicts avibration film etching step, FIG. 6C depicts a film forming step for aconductive film to serve as a lower electrode, FIG. 6D depicts a lowerelectrode forming (conductive film patterning) step, FIG. 6E depicts aconductive film forming step for a first conductive portion, and FIG. 6Fdepicts a first conductive portion forming (conductive film patterning)step.

FIG. 7A depicts a piezoelectric material film forming step, FIG. 7Bdepicts a mask forming step, FIG. 7C depicts a piezoelectric bodyforming (piezoelectric film patterning) step, FIG. 7D depicts aconductive film forming step for an upper electrode, FIG. 7E depicts anupper electrode forming (conductive film patterning) step, and FIG. 7Fdepicts an auxiliary electrode forming step and a wiring forming step.

FIG. 8A depicts an etching step for a flow passage forming member, FIG.8B depicts a joining step for a nozzle plate, and FIG. 8C depicts ajoining step for a reservoir forming member.

FIGS. 9A to 9C depict a part of a head unit according to a modifiedembodiment, wherein FIG. 9A is a top view illustrating the part of thehead unit, FIG. 9B is a sectional view taken along a line IXB-IXB inFIG. 9A, and FIG. 9C is a sectional view taken along a line IXC-IXC inFIG. 9A.

FIGS. 10A to 10C depict a part of a head unit according to anothermodified embodiment, wherein FIG. 10A is a top view illustrating thepart of the head unit, FIG. 10B depicts a sectional view taken along aline XB-XB in FIG. 10A, and FIG. 10C depicts a sectional view takenalong a line XC-XC in FIG. 10A.

FIGS. 11A and 11B depict a part of a head unit according to stillanother modified embodiment, wherein FIG. 11A is a top view illustratingthe part of the head unit, and FIG. 11B is a sectional view taken alonga line XIB-XIB in FIG. 11A.

FIGS. 12A to 12C depict a part of a head unit according to still anothermodified embodiment, wherein FIG. 12A is a top view illustrating thepart of the head unit, FIG. 12B is a sectional view taken along a lineXIIB-XIIB in FIG. 12A, and FIG. 12C is a sectional view taken along aline XIIC-XIIC in FIG. 12A.

FIGS. 13A and 13B depict an upper electrode forming step according tostill another modified embodiment, wherein FIG. 13A depicts a conductivefilm forming step, and FIG. 13B depicts a conductive film patterningstep.

FIG. 14 is a sectional view illustrating a head unit according to stillanother modified embodiment.

FIG. 15 is a sectional view illustrating a head unit according to stillanother modified embodiment corresponding to FIG. 4.

FIG. 16 is a sectional view illustrating a head unit according to stillanother modified embodiment corresponding to FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Next, an embodiment of the present teaching will be explained. At first,an explanation will be made with reference to FIG. 1 about a schematicarrangement of an ink-jet printer 1. Note that the respective directionsof the front, rear, left, and right depicted in FIG. 1 are defined asthe “front”, “rear”, “left”, and “right” of the printer. Further, thefront side of the paper surface is defined as “upper side” or “upside”,and the back side of the paper surface is defined as “lower side” or“downside”. The following explanation will be made while appropriatelyusing the terms concerning the respective directions of front, rear,left, right, upside, and downside.

<Schematic Arrangement of Printer>

As depicted in FIG. 1, the ink-jet printer 1 is provided with, forexample, a platen 2, a carriage 3, an ink-jet head 4, a conveyancemechanism 5, and a controller 6.

Recording paper 100, which is the recording medium, is placed on theupper surface of the platen 2. The carriage 3 is constructed to bereciprocatively movable in the left-right direction (hereinafterreferred to as “scanning direction” as well) along two guide rails 10,11 in the area opposed to the platen 2. An endless belt 14 is connectedto the carriage 3. The endless belt 14 is driven by a carriage drivingmotor 15, and thus the carriage 3 is moved in the scanning direction.

The ink-jet head 4 is attached to the carriage 3, and the ink-jet head 4is movable in the scanning direction together with the carriage 3. Theink-jet head 4 is provided with four head units 16 which are aligned inthe scanning direction. The four head units 16 are connected to acartridge holder 7 to which ink cartridges 17 of four colors (black,yellow, cyan, and magenta) are installed, by means of unillustratedtubes respectively. Each of the head units 16 has a plurality of nozzles24 (see FIGS. 2 to 4) which are formed on the lower surface thereof(surface disposed on the back side as viewed in FIG. 1). The ink, whichis supplied from the ink cartridge 17, is discharged by the nozzles 24of each of the head units 16 toward the recording paper 100 placed onthe platen 2.

The conveyance mechanism 5 has two conveyance rollers 18, 19 which arearranged to interpose the platen 2 therebetween in the front-backdirection. The conveyance mechanism 5 conveys the recording paper 100placed on the platen 2 in the forward direction (hereinafter referred toas “conveyance direction” as well) by means of the two conveyancerollers 18, 19.

The controller 6 is provided with ROM (Read Only Memory), RAM (RandomAccess Memory), and ASIC (Application Specific Integrated Circuit)including various control circuits. The controller 6 executes variousprocesses including, for example, the printing on the recording paper100 by means of ASIC in accordance with programs stored in ROM. Forexample, in the printing process, the controller 6 prints, for example,an image on the recording paper 100 by controlling, for example, theink-jet head 4 and the carriage driving motor 15 on the basis of theprinting instruction inputted from an external apparatus such as PC orthe like. Specifically, the controller 6 alternatively executes the inkdischarge operation in which the inks are discharged while moving theink-jet head 4 in the scanning direction together with the carriage 3,and the conveyance operation in which the recording paper 100 isconveyed by a predetermined amount in the conveyance direction by meansof the conveyance rollers 18, 19.

<Details of Ink-Jet Head>

Next, an explanation will be made about the detailed construction of theink-jet head 4. Note that all of the four head units 16 of the ink-jethead 4 are identically constructed. Therefore, one of them will beexplained, and the other head units 16 are omitted from the explanation.

As depicted in FIGS. 2 to 4, the head unit 16 is provided with a nozzleplate 20, a flow passage forming member 21, a piezoelectric actuator 22,and a reservoir forming member 23. Note that in FIG. 2, the reservoirforming member 23, which is positioned over or above the flow passageforming member 21 and the piezoelectric actuator 22, is depicted byalternate long and two short dashes lines to depict only an outer shapethereof in order to simplify the drawing. Further, in FIGS. 2 and 3, COF50, which is clearly depicted in FIG. 4, is depicted by alternate longand two short dashes lines.

<Nozzle Plate>

The nozzle plate 20 is formed of, for example, a metal material such asstainless steel or the like, silicon, or a synthetic resin material suchas polyimide or the like. The plurality of nozzles 24 are formed for thenozzle plate 20. As depicted in FIG. 2, the plurality of nozzles 24,which discharge one color ink, are arranged in the conveyance directionto construct two arrays of nozzle arrays 25 a, 25 b which are aligned inthe left-right direction. As for the two arrays of the nozzle arrays 25a, 25 b, the positions of the nozzles 24 in the conveyance direction aredeviated by a half (P/2) of the arrangement pitch of each of the nozzlearrays 25.

<Flow Passage Forming Member>

The flow passage forming member 21 is formed of silicon. The nozzleplate 20 described above is joined to the lower surface of the flowpassage forming member 21. A plurality of pressure chambers 26, whichare communicated with the plurality of nozzles 24 respectively, areformed for the flow passage forming member 21. Each of the pressurechambers 26 has a rectangular planner shape which is long in thescanning direction. The plurality of pressure chambers 26 are arrangedin the conveyance direction corresponding to the arrangement of theplurality of nozzles 24 described above to construct two arrays ofpressure chamber arrays.

<Piezoelectric Actuator>

The piezoelectric actuator 22 applies the discharge energy to the inkcontained in the plurality of pressure chambers 26 in order to dischargethe ink from the nozzles 24 respectively. The piezoelectric actuator 22is arranged on the upper surface of the flow passage forming member 21.As depicted in FIGS. 2 to 4, the piezoelectric actuator 22 has such astructure that a plurality of films, which include, for example, avibration film 30, a plurality of lower electrodes 31, a piezoelectricbody 32, and an upper electrode 33, are stacked. Note that the pluralityof films, which constitute the piezoelectric actuator 22, are formed byperforming the film formation and the etching in accordance with anyknown semiconductor process technique on the upper surface of thesilicon substrate to be formed into the flow passage forming member 21as described later on as well.

The vibration film 30 is arranged in the entire region of the uppersurface of the flow passage forming member 21 so that the plurality ofpressure chambers 26 are covered therewith. The vibration film 30 isformed of, for example, silicon dioxide (SiO₂) or silicon nitride(SiNx). A plurality of communication holes 30 a are formed at positionsof the vibration film 30 overlapped with end portions of the pluralityof pressure chambers 26 respectively. The plurality of pressure chambers26 are communicated with the flow passage in the reservoir formingmember 23 described later on respectively by the aid of the plurality ofcommunication holes 30 a.

The plurality of lower electrodes 31 are arranged in areas of the uppersurface of the vibration film 30 overlapped with the pressure chambers26 respectively. That is, the lower electrodes 31 are individualelectrodes which are provided individually with respect to the pressurechambers 26. The shape of the lower electrode 31 is not specificallylimited. However, FIG. 3 depicts the lower electrodes 31 havingrectangular planar shapes smaller than the pressure chambers 26. Asviewed from an upper position, a connecting portion 31 a, which isprovided at one end portion of the lower electrode 31 in thelongitudinal direction, protrudes on the side opposite to thecommunication hole 30 a with respect to the corresponding pressurechamber 26, and connecting portion 31 a is connected to a wiring 35 asdescribed later on. In particular, the lower electrode 31 has a mainelectrode portion 31 b which is arranged in the area opposed to thepressure chamber 26, the connecting portion 31 a which is connected tothe wiring 35, and a linking portion 31 which links the main electrodeportion 31 b and the connecting portion 31 a. The linking portion 31 cis disposed outside the edge of the pressure chamber 26. Further, thepart of the linking portion 31 c (a small width portion 31 d), which isdisposed on the side of the main electrode portion 31 b, has the widthin the direction orthogonal to the scanning direction (extendingdirection of the linking portion 31 c) which is smaller than those ofthe main electrode portion 31 b and the connecting portion 31 a. Thematerial of the lower electrode 31 is not specifically limited. However,the lower electrode 31 can be formed of, for example, platinum (Pt).Further, the lower electrode 31 is not limited to the one layerstructure. It is also allowable to adopt a structure in which aplurality of layers composed of different metals respectively isstacked.

As depicted in FIG. 2, the two piezoelectric bodies 32 are provided onthe upper surface of the vibration film 30 corresponding to the twoarrays of the pressure chamber arrays respectively. The shapes of therespective piezoelectric bodies 32 are not specifically limited as well.However, FIG. 2 depicts those having rectangular planar shapes which arelong in the conveyance direction. Further, as depicted in FIG. 4, theside surface of each of the piezoelectric bodies 32 is inclined inwardlywith respect to the plane orthogonal to the vibration film 30. Thepiezoelectric body 32 has a tapered cross-sectional shape in which theupper surface is smaller than the lower surface. The piezoelectric body32 is composed of, for example, a piezoelectric material containing amain component of lead titanate zirconate (PZT) which is a mixed crystalof lead titanate and lead zirconate. Alternatively, the piezoelectricbody 32 may be formed of a non-lead-based piezoelectric material inwhich no lead is contained.

Each of the piezoelectric bodies 32 is stacked on the plurality of lowerelectrodes 31 to extend over the plurality of lower electrodes 31corresponding to one array of the pressure chamber array in theconveyance direction. In particular, the piezoelectric body 32 coversthe main electrode portion 31 b and the linking portion 31 c of thelower electrode 31. Further, the piezoelectric body 32 is not overlappedwith the connecting portion 31 a of the lower electrode 31. In otherwords, the lower electrode 31 extends in the scanning direction so thata part thereof (connecting portion 31 a) slightly protrudes from thepiezoelectric body 32. The connecting portion 31 a of the lowerelectrode 31, which protrudes from the piezoelectric body 32, isconnected to the wiring 35 as described later on.

Note that as depicted in FIG. 3, a cutout 32 a is formed on the sidesurface (right side surface as viewed in FIG. 3) of the end portion 32 bof the piezoelectric body 32 disposed on the side of the connectingportion 31 a. The cutout 32 a is formed in a groove-shaped formextending in the thickness direction of the piezoelectric body 32 on theside surface of the piezoelectric body 32. The reason, why the cutout 32a is formed for the piezoelectric body 32, will be described in detaillater on in the explanation of the production steps.

The two upper electrodes 33 are formed on the upper surfaces of the twopiezoelectric bodies 32 respectively. Each of the upper electrodes 33 isarranged in the conveyance direction to extent over the plurality oflower electrodes 31. That is, the upper electrode 33 is the commonelectrode which is commonly opposed to the plurality of lower electrodes31 aligned in the conveyance direction. Further, as depicted in FIGS. 2and 3, each of the upper electrodes 33 is arranged in the entire regionin the longitudinal direction of the piezoelectric body 32 so that eachof the upper electrodes 33 is opposed to the main electrode portions 31b of the plurality of lower electrodes 31 with the piezoelectric body 32intervening therebetween on the upper surface of the piezoelectric body32. Further, the upper electrode 33 is also opposed to small widthportions 31 d having small widths of the linking portions 31 c of thelower electrodes 31 with the piezoelectric body 32 interveningtherebetween. However, as depicted in FIGS. 3 and 4, the upper electrode33 is not arranged at the end portion 32 b of the piezoelectric body 32(right end portion as viewed in FIG. 3) disposed on the side of theconnecting portion 31 a. Note that the material of the upper electrode33 is not specifically limited. However, the upper electrode 33 can beformed of, for example, iridium (Ir).

As depicted in FIGS. 3 and 4, two auxiliary electrodes 34, which extendin a lengthy manner in the conveyance direction, are providedrespectively at the both end portions in the widthwise direction of oneupper electrode 33 which extends in the conveyance direction. Theauxiliary electrode 34 is formed of, for example, gold (Au). Althoughthe width of the auxiliary electrode 34 is smaller than that of theupper electrode 33, the thickness is considerably large. If the upperelectrode 33, which is arranged on the upper surface of thepiezoelectric body 32, is thick, the deformation of the piezoelectricbody 32 is inhibited. Therefore, it is preferable that the thickness ofthe upper electrode 33 is thin. However, if the thickness of the upperelectrode 33 as the common electrode is thin, then the electricalresistance of the common electrode is increased, and any problem occurs,for example, such that the electric potential of the common electrode isunstable. In relation thereto, when the two auxiliary electrodes 34having the large thicknesses are provided at the both end portions inthe widthwise direction of the upper electrode 33, it is therebypossible to decrease the electrical resistance of the entire commonelectrode, while decreasing the inhibition of the deformation of thepiezoelectric body 32.

Note that the portions of the piezoelectric body 32, which areinterposed between the plurality of lower electrodes 31 and the upperelectrode 33, are polarized in the downward direction in the thicknessdirection, i.e., in the direction directed from the upper electrode 33to the lower electrodes 31 respectively.

As depicted in FIGS. 3 and 4, a first conductive portion 36, which has ashape different from that of the lower electrode 31, is provided betweenthe lower electrode 31 and the end portion 32 b of the piezoelectricbody 32 which covers the lower electrode 31. In particular, the firstconductive portion 36 is overlapped with the lower electrode 31 so thatthe first conductive portion 36 extends over the region ranging from theconnecting portion 31 a up to the neighboring portion 31 e which is theportion of the linking portion 31 c adjoined to the connecting portion31 a. In this case, the neighboring portion 31 e of the linking portion31 c can be also defined as the area of the lower electrode 31overlapped with the end portion 32 b of the piezoelectric body 32. Asdepicted in FIG. 3, the first conductive portion 36 is arranged on theouter side as compared with the edge of the pressure chamber 26 in thescanning direction and on the outer side as compared with the smallwidth portion 31 d of the lower electrode 31 (on the side of theconnecting portion 31 a). Further, the first conductive portion 36 isarranged on the outer side in the scanning direction as compared withthe end portion (right end portion as viewed in FIG. 3) of the upperelectrode 33 in the scanning direction. Note that in this embodiment, asdepicted in FIGS. 3 to 5, the first conductive portion 36 covers theentire upper surface of the connecting portion 31 a of the lowerelectrode 31. In other words, as viewed from an upper position, thefirst conductive portion 36 is larger than the connecting portion 31 aof the lower electrode 31.

As depicted in FIGS. 2 to 4, the plurality of wirings 35, which areconnected to the plurality of lower electrodes 31 respectively, areformed on the upper surface of the vibration film 30. Each of thewirings 35 is formed in the region ranging from the upper surface of theend portion the piezoelectric body 32 disposed on the side of theconnecting portion 31 a to the side surface of the piezoelectric body 32and the surface of the first conductive portion 36. That is, the wiring35 makes conduction with the connecting portion 31 a of the lowerelectrode 31 by the aid of the first conductive portion 36. Note that inthis embodiment, as depicted in FIG. 4, the end portion of the wiring 35is formed to overhang up to the upper surface of the piezoelectric body32. Accordingly, the contact area between the wiring 35 and thepiezoelectric body 32 is increased, and the application of any locallyhigh electric field to the piezoelectric body 32 is mitigated.Therefore, the piezoelectric body 32 is suppressed from the occurrenceof any crack.

Further, each of the wirings 35 extends in the scanning direction fromthe connecting portion 31 a of the lower electrode 31. In particular, asdepicted in FIG. 2, the wirings 35, which are connected to the lowerelectrodes 31 arranged on the left side, extend to the left from thecorresponding lower electrodes 31. The wirings 35, which are connectedto the lower electrodes 31 arranged on the right side, extend to theright from the corresponding lower electrodes 31. Note that each of thewirings 35 is formed of, for example, gold (Au) or aluminum (Al).

In the meantime, the reason, why the first conductive portion 36 isprovided for the connecting portion 31 a of the lower electrode 31connected to the wiring 35, is as follows. As described later on, in thesteps of manufacturing the piezoelectric actuator 22, a piezoelectricmaterial film 62 is formed as a film on the lower electrode 31, and thepiezoelectric material film 62 is subjected to the patterning by meansof the etching to form the piezoelectric body 32 (see FIG. 7). In thisprocedure, when the piezoelectric material film 62 is etched, it isfeared that the connecting portion 31 a of the lower electrode 31 andthe neighboring portion thereof may be removed together. In relationthereto, in this embodiment, the first conductive portion 36 issuperimposed on the lower electrode 31, and the connecting portion 31 aof the lower electrode 31 is covered with the first conductive portion36. Therefore, the first conductive portion 36 prevents such a situationthat the connecting portion 31 a is scraped off and the electrodethickness is thinned. The reliability of the electric connection ismaintained between the connecting portion 31 a and the wiring 35.

The conductive material, which forms the first conductive portion 36, isnot limited to any specified material. It is possible to adopt variousmaterials. However, it is preferable that the material of the firstconductive portion 36 is selected in accordance with any one of thefollowing viewpoints (1) to (3).

(1) As also explained later on as well, when the piezoelectric materialfilm 62 is subjected to the patterning especially by means of the dryetching, it is feared that the first conductive portion 36 may bescraped off and removed together on account of the physical etchingaction of the dry etching. Accordingly, it is preferable that the firstconductive portion 36 is formed of a metal which is harder than thelower electrode 31 so that the first conductive portion 36 is hardlyscraped off when the piezoelectric material film 62 is subjected to thedry etching. For example, it is preferable that the first conductiveportion 36 is formed of a hard metal including, for example, tantalum(Ta), tungsten (W), and iridium (Ir). Table 1 shows the Mohs hardness,the Vickers hardness, and the Brinell hardness in relation to W, Ta, andIr respectively as the materials for forming the first conductiveportion 36.

TABLE 1 Metal Mohs Vickers Brinell material hardness hardness hardnessPt 4 to 4.5  549 MPa  392 MPa W 7.5 3430 MPa 2570 MPa Ta 6.5  873 MPa 800 MPa Ir 6.5 1760 MPa 1670 MPa

(2) When the first conductive portion 36 and the wiring 35 are formed ofmutually different materials, the electrical resistance greatly differsat the boundary between the both. In this viewpoint, it is preferablethat the first conductive portion 36 is formed of the same conductivematerial (for example, gold or aluminum) as that of the wiring 35.

(3) A part of the metal material contained in the first conductiveportion 36 may be diffused into the piezoelectric body 32 in some cases.In accordance therewith, if the composition of the piezoelectric body 32is changed, the piezoelectric characteristic is changed as well. In viewof the above, it is preferable that the first conductive portion 36 isformed of a metal material which hardly affects the characteristic ofthe piezoelectric body 32.

In this viewpoint, it is preferable that the metal element, whichconstitutes the piezoelectric body 32, is not contained in the firstconductive portion 36. For example, when the piezoelectric body 32 iscomposed of a piezoelectric material containing a main component of leadtitanate zirconate (PZT), it is preferable that at least titanium (Ti),zirconia (Zr), and lead (Pb) are not contained in the first conductiveportion 36.

As depicted in FIG. 2, each of the left and right both end portions ofthe flow passage forming member 21 (vibration film 30) is an electricjoining portion 39 to which COF (Chip On Film) 50 as a wiring member isjoined. Specifically, the plurality of wirings 35, which are led outleftwardly from the array of the lower electrodes 31 disposed on theleft side, extend up to the electric joining portion 39 disposed on theleft side. Further, the plurality of wirings 35, which are led outrightwardly from the array of the lower electrodes 31 disposed on theright side, extend up to the electric joining portion 39 disposed on theright side. Then, a plurality of driving contact portions 40, which areprovided at the end portions of the plurality of wirings 35, arearranged at the electric joining portion 39 while being aligned in theconveyance direction. Further, two ground contact portions 41 are alsoarranged at each of the electric joining portions 39. Wirings 38, whichare led out from the upper electrode 33, are connected to the respectiveground contact portions 41.

As depicted in FIGS. 2 to 4, two COF's 50 are joined respectively to thetwo electric joining portions 39 of the piezoelectric actuator 22described above. Then, a plurality of wirings 55, which are formed oneach COF 50, are electrically connected to the plurality of drivingcontact portions 40 respectively. Although not depicted in the drawing,each COF 50 is also connected to the controller 6 of the printer 1 (seeFIG. 1).

Driver IC 51 is mounted on each COF 50. The driver IC generates andoutputs the driving signal for driving the piezoelectric actuator 22 onthe basis of the control signal sent from the controller 6. The drivingsignal, which is outputted from the driver IC 51, is inputted into thedriving contact portion 40 via the wiring 55 of COF 50. Further, thedriving signal is supplied to each of the lower electrodes 31 via thewiring 35 of the piezoelectric actuator 22. The lower electrode 31, towhich the driving signal is supplied, has the electric potential whichchanges between a predetermined driving electric potential and theground electric potential. Further, a ground wiring (not depicted) isalso formed for COF 50. The ground wiring is electrically connected tothe ground contact portion 41 of the piezoelectric actuator 22.Accordingly, the upper electrode 33, which is connected to the groundcontact portion 41, has the electric potential which is alwaysmaintained at the ground electric potential.

An explanation will be made about the operation of the piezoelectricactuator 22 when the driving signal is supplied from the driver IC 51.In the state in which the driving signal is not supplied, the electricpotential of the lower electrode 31 is the ground electric potential,which is the same as the electric potential of the upper electrode 33.Starting from this state, when the driving signal is supplied to acertain lower electrode 31, and the driving electric potential isapplied to the lower electrode 31, then the electric field, which isparallel to the thickness direction, acts on the piezoelectric body 32in accordance with the electric potential difference between the lowerelectrode 31 and the upper electrode 33. In this situation, thedirection of polarization of the piezoelectric body 32 is coincidentwith the direction of the electric field. Therefore, the piezoelectricbody 32 is elongated in the thickness direction which is the directionof polarization thereof, and the piezoelectric body 32 is shrunk in thein-plane direction (surface direction). The vibration film 30 is warpedor flexibly bent so that the vibration film 30 protrudes toward thepressure chamber 26 in accordance with the shrinkage deformation of thepiezoelectric body 32. Accordingly, the volume of the pressure chamber26 is decreased, and the pressure wave is generated in the pressurechamber 26. Thus, the droplets of the ink are discharged from the nozzle24 communicated with the pressure chamber 26.

<Reservoir Forming Member>

As depicted in FIGS. 4 and 5, the reservoir forming member 23 isarranged on the side (upside) opposite to the flow passage formingmember 21 with the piezoelectric actuator 22 intervening therebetween,and the reservoir forming member 23 is joined to the upper surface ofthe piezoelectric actuator 22 by using an adhesive. The reservoirforming member 23 may be formed of, for example, silicon in the samemanner as the flow passage forming member 21. However, the reservoirforming member 23 may be formed of any material other than silicon, forexample, a metal material or a synthetic resin material.

As depicted in FIG. 4, a reservoir 52, which extends in the conveyancedirection, is formed at an upper half portion of the reservoir formingmember 23. Each of the reservoirs 52 is connected via an unillustratedtube to the cartridge holder 7 (see FIG. 1) to which the ink cartridges17 are installed.

A plurality of ink supply flow passages 53, which extends downwardlyfrom the reservoir 52, is formed at a lower half portion of thereservoir forming member 23. The respective ink supply flow passages 53are communicated with the plurality of communication holes 30 a whichare formed through the vibration film 30 of the piezoelectric actuator22. Accordingly, the ink is supplied from the reservoir 52 via theplurality of ink supply flow passages 53 and the plurality ofcommunication holes 30 a to the plurality of pressure chambers 26 of theflow passage forming member 21. Further, a recessed protective coverportion 54, which covers the plurality of piezoelectric bodies 32 of thepiezoelectric actuator 22, is also formed at the lower half portion ofthe reservoir forming member 23.

Next, an explanation will be made with reference to FIGS. 6 to 8 aboutthe manufacturing steps of the head unit 16 of the ink-jet head 4described above, especially principally about the manufacturing steps ofthe piezoelectric actuator 22. FIGS. 6 to 8 illustrate the manufacturingsteps of the ink-jet head respectively.

In this embodiment, the piezoelectric actuator 22 is produced bystacking various films in accordance with the semiconductor processincluding, for example, the film formation and the patterning on theflow passage forming member 21 as the silicon substrate. At first, asdepicted in FIG. 6A, the vibration film 30 of silicon dioxide or thelike is formed as a film on the surface of the flow passage formingmember 21 as the silicon substrate. Further, as depicted in FIG. 6B, thecommunication holes 30 a are formed through the vibration film 30 bymeans of the etching.

Subsequently, the plurality of lower electrodes 31 are formed on thevibration film 30. At first, as depicted in FIG. 6C, a conductive film60 for the lower electrodes 31 is formed, for example, by means of thesputtering on the vibration film 30. Then, as depicted in FIG. 6D, theconductive film 60 is subjected to the patterning by means of theetching, and thus the plurality of lower electrodes 31 are formed.

Subsequently, the first conductive portions 36 are formed for theplurality of lower electrodes 31 respectively. As depicted in FIG. 6E, aconductive film 61 for the first conductive portions 36 is formed on thevibration film 30, for example, by means of the sputtering so that theplurality of lower electrodes 31 are covered therewith. Then, asdepicted in FIG. 6F, the conductive film 61 is subjected to thepatterning by means of the etching, and thus the first conductiveportions 36 are formed so that the connecting portions 31 a of the lowerelectrodes 31 and the neighboring portions thereof are coveredtherewith.

Subsequently, the piezoelectric body 32 is formed on the plurality oflower electrodes 31. At first, as depicted in FIG. 7A, a piezoelectricmaterial film 62 is formed as a film by means of the sol-gel method orthe sputtering in the entire region of the upper surface of thevibration film 30 so that the lower electrodes 31 and the firstconductive portions 36 are covered therewith. Subsequently, as depictedin FIG. 7B, a mask 63 of resist pattern, which corresponds to the shapeof the piezoelectric body 32, is formed on the piezoelectric materialfilm 62. After that, unnecessary portions of the piezoelectric materialfilm 62 are removed by means of the dry etching to perform thepatterning so that the piezoelectric body 32 is formed. Note that whenthe unnecessary portions of the piezoelectric material film 62 areremoved by means of the dry etching, the side surfaces of thepiezoelectric body 32 are formed to provide such shapes that the sidesurfaces are inclined inwardly with respect to the plane orthogonal tothe vibration film 30.

An explanation will be supplemented about the dry etching for thepiezoelectric material film 62. When the flow passage forming member 21,which is formed with the piezoelectric material film 62 as the film, isinstalled in a chamber of an etching apparatus, and the plasma isgenerated after enclosing the carrier gas in the chamber, then the ionis accelerated in the chamber, and the ion collides with thepiezoelectric material film 62. For example, a mixed gas, which containshalogen-based gas (for example, CHF₃, SF₆, BCl₃, Cl₂) and any one ofoxygen, nitrogen, and argon (Ar), is used, and the dry etching isperformed in the chamber in the plasma atmosphere at a chamber pressureof 0.5 to 50 Pa.

In the case of the general dry etching, the etching advances inaccordance with the actions of both of the physical etching based on thecollision of the ion and the chemical etching based on the chemicalreaction between the ion and the processing objective. However, in thecase of the etching for the piezoelectric material such as PZT or thelike, the chemical etching hardly advances, for example, for such areason that the reaction product, which is produced by the chemicalreaction, has the low volatility, and the physical etching principallyoccurs. In other words, the etching for the piezoelectric material film62 advances in such a form that the piezoelectric material is scrapedoff by the energy generated when the ion collides.

Therefore, when the portions of the piezoelectric material film 62,which cover the connecting portions 31 a, are removed by means of thedry etching for the piezoelectric material film 62, it is feared thatthe connecting portions 31 a of the lower electrodes 31, which aredisposed thereunder or therebelow, may be scraped off and removedtogether in accordance with the physical etching action. In thisprocedure, if the connecting portions 31 a of the lower electrodes 31,which protrude from the piezoelectric body 32, are scraped off, and theelectrode thickness is thinned at the portions, then the reliability ofthe electrical connection is lowered between the connecting portions 31a and the wirings 35. However, in this embodiment, the first conductiveportion 36 is superimposed to cover the connecting portion 31 aprotruding from the piezoelectric body 32 and the neighboring portion ofthe connecting portion 31 a covered with the piezoelectric body 32, andthe connecting portion 31 a and the neighboring portion thereof areprotected by the first conductive portion 36. Therefore, such asituation is suppressed that the lower electrode 31 is scraped off bythe dry etching for the piezoelectric material 62 and the electrodethickness is thinned. The reliability of the electrical connection ismaintained between the lower electrode 31 and the wiring 35. Further,when the first conductive portion 36 is formed of the material harderthan the lower electrode 31, then the first conductive portion 36 ishardly scraped off during the dry etching for the piezoelectric materialfilm 62, and the reliability of the electrical connection with respectto the wiring 35 is enhanced.

Note that with reference to FIG. 7B, the mask 63, which is used for thedry etching, is formed with cutouts 63 a which are disposed at portionsoverlapped with the first conductive portions 36 when the mask isinstalled on the upper surface of the piezoelectric material film 62.The cutout 63 a is open laterally (on the right side in the drawing),and the cutout 63 a has a groove shape extending in the thicknessdirection of the mask 63. The cutouts 63 a are formed for the mask 63,and hence the cutouts 32 a (see FIG. 3) are also formed on the sidesurface of the end portion 32 b of the piezoelectric body 32 by means ofthe dry etching. However, the provision of the cutouts 63 a for the mask63 is not principally aimed to form the cutouts 32 a for thepiezoelectric body 32. When the cutouts 63 a are formed for the mask 63,then the piezoelectric material film 62 is hardly etched and the etchingspeed is lowered at the inside of the cutouts 63 a as compared with theother areas which are not covered with the mask 63. In other words, whenthe etching is performed for the piezoelectric material film 62, thespeed of advance of the etching is slow at the inside of the cutout 63 aof the mask 63. Therefore, the connecting portion 31 a and the firstconductive portion 36 are hardly removed, and they remain with ease.Therefore, the reliability of the electrical connection is improvedbetween the wiring 35 and the connecting portion 31 a of the lowerelectrode 31 as compared with a case in which the mask 63 has no cutout63 a.

After the formation of the piezoelectric body 32, the upper electrodes33 are formed on the upper surface of the piezoelectric body 32. Asdepicted in FIG. 7D, a conductive film 64 for the upper electrode 33 isformed as a film, for example, by means of the sputtering on the uppersurface of the vibration film 30 and the upper surface of thepiezoelectric body 32. After that, as depicted in FIG. 7E, theconductive film 64 is subjected to the patterning by means of theetching to form the upper electrode 33. After that, as depicted in FIG.7F, the two auxiliary electrodes 34 are formed on the upper surface ofthe upper electrode 33. Further, the wirings 35, which extend from theupper surface to the side surface of the piezoelectric body 32 and tothe first conductive portions 36, are formed. When the material (forexample, gold (Au)) of the auxiliary electrodes 34 is the same as thatof the wirings 35, the auxiliary electrodes 34 and the wirings 35 can beformed in the same step. That is, a conductive film of gold is formed asa film, and the conductive film is subjected to the patterning by meansof the etching. Thus, the auxiliary electrodes 34 and the wirings 35 areformed in a separated manner. In accordance with the steps as describedabove, the production of the piezoelectric actuator 22 is completed.

As depicted in FIG. 8A, the pressure chambers 26 are formed byperforming the etching from the lower surface side of the flow passageforming member 21 disposed on the side opposite to the piezoelectricactuator 22. Further, as depicted in FIG. 8B, the nozzle plate 20 isjoined by using an adhesive to the lower surface of the flow passageforming member 21. Finally, as depicted in FIG. 8C, the reservoirforming member 23 is joined to the piezoelectric actuator 22 by using anadhesive.

In the embodiment explained above, the vibration film 30, which isprovided for the flow passage forming member 21, corresponds to the“substrate” according to the present teaching. The lower electrode 31,which is positioned on the lower side of the piezoelectric body 32,corresponds to the “first electrode” according to the present teaching.The upper electrode 33, which is positioned on the upper side of thepiezoelectric body 32, corresponds to the “second electrode” accordingto the present teaching.

Next, an explanation will be made about modified embodiments in whichvarious modifications are applied to the embodiment described above.However, those constructed in the same manner as those of the embodimentdescribed above are designated by the same reference numerals, and anyexplanation thereof will be appropriately omitted.

(1) As depicted in FIGS. 9A to 9C, a second conductive portion 70, whichis formed of the same material as that of the first conductive portion36, may be arranged for the electric joining portion 39 of the flowpassage forming member 21 (vibration film 30). The second conductiveportion 70 can be simultaneously formed in accordance with the same stepas that for the first conductive portion 36. When the second conductiveportion 70 is provided on the lower side of the wiring 35 (drivingcontact portion 40) in the electric joining portion 39, the drivingcontact portion 40, which covers the second conductive portion 70, risesthereby as compared with the surroundings. Accordingly, when COF 50 isjoined to the driving contact portion 40 of the electric joining portion39, then COF 50 can be strongly pressed against the driving contactportion 40 locally, and the reliability of the joining is enhanced.Further, as depicted in FIG. 9C, it is preferable that thecross-sectional shape of the second conductive portion 70 is such atapered shape that the cross-sectional shape is more tapered atpositions disposed farther on the upper side (side opposite to thevibration film 30). Accordingly, a part of the wiring 35 (drivingcontact portion 40) to cover the second conductive portion 70 locallyprotrudes, and hence COF 50 can be pressed thereagainst more strongly.The reliability of the joining is further improved.

The following modifications can be further applied to the embodimentdepicted in FIGS. 9A to 9C. At first, as depicted in FIGS. 10A to 10C,the connecting portion 31 a of the lower electrode 31 may extend up tothe electric joining portion 39. In this case, the connecting portion 31a of the lower electrode 31 is arranged under or below the wiring 35extending to the electric joining portion 39. Therefore, the wiring 35is substantially thickened, and the conduction reliability of the wring35 is improved. Further, as depicted in FIGS. 11A and 11B, the firstconductive portion 36 may also extend up to the electric joining portion39 together with the connecting portion 31 a of the lower electrode 31,and the first conductive portion 36 and the second conductive portion 70may make conduction. In this case, the substantial thickness of thewiring 35 is further thickened, and hence the conduction reliability ofthe wring 35 is further improved.

(2) In the embodiment described above, as depicted in FIGS. 4 and 5, thefirst conductive portion 36 is arranged so that the upper surface of theconnecting portion 31 a of the lower electrode 31 is covered therewith.In contrast thereto, as depicted in FIGS. 12A to 12C, it is alsoallowable to adopt a form in which the first conductive portion 36 andthe lower electrode 31 are arranged upside down, i.e., a form in whichthe lower electrode 31 covers the upper surface of the first conductiveportion 36. In this case, even when a part of the connecting portion 31a of the lower electrode 31 is removed when the piezoelectric materialfilm 62 is etched, then the electrical connection between the connectingportion 31 a and the wiring 35 is maintained by the first conductiveportion 36 disposed under or below the connecting portion 31 a.

(3) In the embodiment described above, the patterning for thepiezoelectric material film 62 (see FIG. 7C) is performed by means ofthe dry etching. However, the patterning for the piezoelectric materialfilm 62 can be also performed by means of the wet etching.

(4) In the foregoing embodiment, the piezoelectric material film 62 issubjected to the patterning to form the piezoelectric body 32, and thenthe upper electrode 33 is formed on the upper surface of thepiezoelectric body 32. In the step of forming the upper electrode 33, asdepicted in FIG. 13A, the conductive film 64 is formed as the film tocover the connecting portion 31 a of the lower electrode 31 and thepiezoelectric body 32, and then the conductive film 64 is subjected tothe patterning as depicted in FIG. 13B. In the embodiment describedabove (FIG. 7E), the portion of the conductive film 64, which covers theconnecting portion 31 a, is removed during the patterning. However, itis also assumed that parts of the connecting portion 31 a and the firstconductive portion 36 may be removed during this process. Accordingly,as depicted in FIG. 13B, the portion 64 a (third conductive portion) ofthe conductive film 64, which covers the connecting portion 31 a, may beallowed to remain without being removed after being separated from theupper electrode 33 in the patterning step for the conductive film 64. Inthis case, the connecting portion 31 a of the lower electrode 31 and thefirst conductive portion 36 are not removed by the etching during theformation of the upper electrode 33.

(5) As depicted in FIG. 14, when the wiring 35 has a thin seed layer 35b and a main layer 35 a disposed thereon, if the film thickness of theseed layer 35 b is uneven, then it is feared that the thin seed layer 35b may be divided at any intermediate position. In particular, the sidesurface of the piezoelectric body 32 is such a place that the seed layer35 b hardly adheres, on which the film thickness of the seed layer 35 beasily becomes uneven. In this viewpoint, it is desirable that the sidesurface of the piezoelectric body 32 is a gently inclined surface.Accordingly, it is also preferable that the angle of inclination of theside surface of the piezoelectric body 32 may be made gentler by usingany method such as the reverse sputtering or the like after the sidesurface of the piezoelectric body 32 is formed into the inclined surfaceduring the etching for the piezoelectric material film 62.

(6) In the embodiment described above, as depicted in FIG. 4, the firstconductive portion 36 is provided to extend over from the area of thelower electrode 31 overlapped with the end portion 32 b of thepiezoelectric body 32 up to the connecting portion 31 a on the lowerside of the end portion 32 b of the piezoelectric body 32. Therefore,even if the first conductive portion 36 is scraped off to some extentwhen the piezoelectric material film is etched, then the conduction ismaintained between the lower electrode 31 and the wiring 35. Further, asdepicted in FIG. 15, no problem occurs even when the first conductiveportion 36, which covers the connecting portion 31 a of the lowerelectrode 31, is completely removed by the etching for the piezoelectricmaterial film. In other words, the first conductive portion 36 may beprovided on the lower electrode 31 in the area overlapped with the endportion 32 b of the piezoelectric body 32, only the lower electrode 31may protrude from the end portion 32 b of the piezoelectric body 32, andthe protruding portion may serve as the connecting portion with respectto the wiring 35. Alternatively, as depicted in FIG. 16, in a form inwhich the first conductive portion 36 is arranged on the lower side ofthe lower electrode 31 in the area overlapped with the end portion 32 bof the piezoelectric body 32, no problem occurs even when the portion ofthe lower electrode 31, which covers the first conductive portion 36, iscompletely removed in the area protruding from the end portion 32 b ofthe piezoelectric body 32. In other words, only the first conductiveportion 36 may protrude from the end portion 32 b of the piezoelectricbody 32, and the protruding portion may serve as the connecting portionwith respect to the wiring 35.

(7) If the lower electrode 31 is thick, the deformation of thepiezoelectric body 32 is inhibited by the lower electrode 31 when thevoltage is applied to the piezoelectric body 32. Accordingly, it is alsoappropriate that a thin-walled portion, which has a small thickness ascompared with the surroundings, is formed by the half etching at acentral portion of the lower electrode 31 during the formation of thelower electrode 31 (during the patterning for the conductive film 60)depicted in FIGS. 6C and 6D.

(8) In the embodiment described above, the lower electrode 31, which isdisposed on the lower side (side of the vibration film 30) with respectto the piezoelectric body 32, is the individual electrode, and the upperelectrode 33, which is disposed on the upper side (side opposite to thevibration film 30), is the common electrode. In contrast thereto, thelower electrode 31 may be a common electrode, and the upper electrode 33may be an individual electrode.

(9) The structure of the ink flow passage of the ink-jet head 4 is notlimited to the structure described in the foregoing embodiment. Forexample, the structure can be modified as follows. In the embodimentdescribed above, as depicted in FIG. 4, the flow passage is constructedsuch that the ink is supplied individually from the reservoir 52 in thereservoir forming member 23 via the plurality of communication holes 30a to the plurality of pressure chambers 26 respectively. In contrastthereto, it is also appropriate that any flow passage, which correspondsto the reservoir 52, is formed in the flow passage forming member 21.For example, it is also appropriate that a manifold flow passage, whichextends in the arrangement direction of the plurality of pressurechambers 26, is formed in the flow passage forming member 31, and theink is individually distributed and supplied from one manifold flowpassage to the plurality of pressure chambers 26 in the flow passageforming member 21.

In the embodiment and the modified embodiments explained above, thepresent teaching is applied to the piezoelectric actuator for theink-jet head for printing, for example, an image by discharging the inksonto the recording paper. However, the present teaching is alsoapplicable to any liquid discharge apparatus to be used for various waysof use other than the printing of the image or the like. For example,the present teaching can be also applied to a liquid discharge apparatusfor discharging a conductive liquid onto a substrate to form aconductive pattern on a surface of the substrate. Further, thepiezoelectric actuator of the present teaching is not limited to thoseused in order to apply the pressure to the liquid as well. For example,the present teaching can be also applied, for example, to an actuatorwhich moves a solid object and an actuator which pressurizes a gas.

What is claimed is:
 1. A piezoelectric actuator comprising: a substrate,the substrate having a first end and a second end in a first directionwhich is along a planer direction of the substrate; a first conductivelayer at least partially overlapping with the substrate in a seconddirection which is orthogonal to the planar direction of the substrate,the first conductive layer having a third end and a fourth end in thefirst direction; a second conductive layer at least partiallyoverlapping with the first conductive layer and the substrate in thesecond direction, the second conductive layer having a fifth end and asixth end in the first direction; a piezoelectric body at leastpartially overlapping with the substrate, the first conductive layer,and the second conductive layer in the second direction, thepiezoelectric body having a seventh end and an eighth end in the firstdirection, wherein the first conductive layer is at least partiallypositioned between the piezoelectric body and the substrate in thesecond direction; and a wiring connected to the first conductive layer;wherein the third end of the first conductive layer is positionedbetween the first end of the substrate and the fourth end of the firstconductive layer in the first direction; wherein the fifth end of thesecond conductive layer is positioned between the first end of thesubstrate and the sixth end of the second conductive layer in the firstdirection; wherein the seventh end of the piezoelectric body ispositioned between the first end of the substrate and the eighth end ofthe piezoelectric body in the first direction; wherein the eighth end ofthe piezoelectric body is positioned between the fifth end of the secondconductive layer and the sixth end of the second conductive layer in thefirst direction; wherein the eighth end of the piezoelectric body ispositioned between the third end of the first conductive layer and thefourth of the first conductive layer in the first direction; wherein thefifth end of the second conductive layer is positioned between theseventh end of the piezoelectric body and the eighth end of thepiezoelectric body in the first direction; wherein the fifth end of thesecond conductive layer is positioned between the third end of the firstconductive layer and the fourth end of the first conductive layer in thefirst direction; wherein the second conductive layer comprises a portionextending from the fifth end of the second conductive layer toward theeighth end of the piezoelectric body along the first direction; andwherein the portion of the second conductive layer is located betweenthe piezoelectric body and the substrate in the second direction.
 2. Thepiezoelectric actuator according to claim 1; wherein the secondconductive layer is formed of a conductive material which is harder thanthe first conductive layer.
 3. The piezoelectric actuator according toclaim 1; wherein the second conductive layer is formed of tantalum,tungsten, or iridium.
 4. The piezoelectric actuator according to claim1; wherein the second conductive layer is formed of the same conductivematerial as that of the wiring.
 5. The piezoelectric actuator accordingto claim 1; wherein the second conductive layer is formed of aconductive material which does not contain any metallic elementcontained in the piezoelectric body.
 6. The piezoelectric actuatoraccording to claim 1; wherein the first conductive layer is positionedbetween the second conductive layer and the substrate in the seconddirection.
 7. The piezoelectric actuator according to claim 1; whereinthe second conductive layer is positioned between the first conductivelayer and the substrate in the second direction.
 8. The piezoelectricactuator according to claim 1; wherein the wiring has a ninth end whichis connected to the first conductive layer and a tenth end which iselectrically connected to a wiring member; wherein the wiring extends inthe first direction from the ninth end to the tenth end; wherein a thirdconductive layer, which is formed of the same conductive material asthat of the second conductive layer, is provided between the ninth endof the wiring and the tenth end of the wiring in the first direction;and wherein the third conductive layer is positioned between the wiringand the substrate in the second direction.
 9. The piezoelectric actuatoraccording to claim 8; wherein the first conductive layer is positionedbetween the wiring and the substrate in the second direction; whereinthe second conductive layer extends in the first direction along thewiring; and wherein the second conductive layer is in conduction withthe third conductive layer.
 10. The piezoelectric actuator according toclaim 8; wherein the third conductive layer has such a shape that thecross-sectional shape thereof is tapered in the second direction. 11.The piezoelectric actuator according to claim 1; further comprising: anelectrode at least partially overlapping with the substrate, the firstconductive layer, and the piezoelectric body in the second direction,wherein the piezoelectric body is positioned between the firstconductive layer and the electrode in the second direction; wherein thefirst conductive layer has a small width portion between the third endof the first conductive layer and the fourth end of the first conductivelayer in the first direction; wherein the small width portion faces theelectrode with the piezoelectric body intervening therebetween; whereinthe small width portion of the first conductive layer is narrower thanthe third end of the first conductive layer and the fourth end of thefirst conductive layer in a third direction which is along the planardirection of the substrate and orthogonal to the first direction; andwherein the fifth end of the second conductive layer is arranged betweenthe small width portion of the first conductive layer and the sixth endof the second conductive layer in the first direction.
 12. Thepiezoelectric actuator according to claim 1; wherein a cutout is formedon a side surface of the eighth end of the piezoelectric body.
 13. Thepiezoelectric actuator according to claim 1, further comprising: anelectrode at least partially overlapping with the substrate, the firstconductive layer, and the piezoelectric body in the second direction,wherein the piezoelectric body is positioned between the firstconductive layer and the electrode in the second direction; and a fourthconductive layer which is formed of the same material as that of theelectrode and which is separated from the electrode; wherein the fourthconductive layer overlaps with the eighth end of the piezoelectric bodyin the second direction; and wherein the eighth end of the piezoelectricbody is positioned between the fourth conductive layer and the secondconductive layer in the second direction.
 14. The piezoelectric actuatoraccording to claim 1, further comprising: an electrode at leastpartially overlapping with the substrate, the first conductive layer,and the piezoelectric body in the second direction, wherein thepiezoelectric body is positioned between the first conductive layer andthe electrode in the second direction; wherein an auxiliary electrode,which is formed of the same material as that of the wiring and which isseparated from the wiring, is provided to overlap with the electrode inthe second direction; and wherein the electrode is positioned betweenthe auxiliary electrode and the piezoelectric body in the seconddirection.
 15. A piezoelectric actuator comprising: a substrate, thesubstrate having a first end and a second end in a first direction whichis along a planer direction of the substrate; a first conductive layerat least partially overlapping with the substrate in a second directionwhich is orthogonal to the planar direction of the substrate, the firstconductive layer having a third end and a fourth end in the firstdirection; a second conductive layer at least partially overlapping withthe first conductive layer and the substrate in the second direction,the second conductive layer having a fifth end and a sixth end in thefirst direction; a piezoelectric body at least partially overlappingwith the substrate, the first conductive layer, and the secondconductive layer in the second direction, the piezoelectric body havinga seventh end and an eighth end in the first direction, wherein thefirst conductive layer is at least partially positioned between thepiezoelectric body and the substrate in the second direction; and awiring connected to the first conductive layer; wherein the third end ofthe first conductive layer is positioned between the first end of thesubstrate and the fourth end of the first conductive layer in the firstdirection; wherein the fifth end of the second conductive layer ispositioned between the first end of the substrate and the sixth end ofthe second conductive layer in the first direction; wherein the seventhend of the piezoelectric body is positioned between the first end of thesubstrate and the eighth end of the piezoelectric body in the firstdirection; wherein the eighth end of the piezoelectric body ispositioned between the third end of the first conductive layer and thefourth end of the first conductive layer in the first direction; whereinthe fifth end of the second conductive layer is positioned between theseventh end of the piezoelectric body and the eighth end of thepiezoelectric body in the first direction; wherein the fifth end of thesecond conductive layer is positioned between the third end of the firstconductive layer and the fourth end of the first conductive layer in thefirst direction; wherein the second conductive layer comprises a portionextending from the fifth end of the second conductive layer toward theeighth end of the piezoelectric body along the first direction; andwherein the portion of the second conductive layer is located betweenthe piezoelectric body and the substrate in the second direction. 16.The piezoelectric actuator according to claim 15; wherein the portion ofthe second conductive layer is positioned between the first conductivelayer and the piezoelectric body in the second direction.
 17. Apiezoelectric actuator comprising: a substrate, the substrate having afirst end and a second end in a first direction which is along a planerdirection of the substrate; a first conductive layer at least partiallyoverlapping with the substrate in a second direction which is orthogonalto the planar direction of the substrate, the first conductive layerhaving a third end and a fourth end in the first direction; a secondconductive layer at least partially overlapping with the firstconductive layer and the substrate in the second direction, the secondconductive layer having a fifth end and a sixth end in the firstdirection; a piezoelectric body at least partially overlapping with thesubstrate, the first conductive layer, and the second conductive layerin the second direction, the piezoelectric body having a seventh end andan eighth end in the first direction, wherein the first conductive layeris at least partially positioned between the piezoelectric body and thesubstrate in the second direction; and a wiring connected to the firstconductive layer; wherein the third end of the first conductive layer ispositioned between the first end of the substrate and the fourth end ofthe first conductive layer in the first direction; wherein the fifth endof the second conductive layer is positioned between the first end ofthe substrate and the sixth end of the second conductive layer in thefirst direction; wherein the seventh end of the piezoelectric body ispositioned between the first end of the substrate and the eighth end ofthe piezoelectric body in the first direction; wherein the eighth end ofthe piezoelectric body is positioned between the fifth end of the secondconductive layer and the sixth end of the second conductive layer in thefirst direction; wherein the fifth end of the second conductive layer ispositioned between the seventh end of the piezoelectric body and theeighth end of the piezoelectric body in the first direction; wherein thefifth end of the second conductive layer is positioned between the thirdend of the first conductive layer and the fourth end of the firstconductive layer in the first direction; wherein the second conductivelayer comprises a portion extending from the fifth end of the secondconductive layer toward the eighth end of the piezoelectric body alongthe first direction; and wherein the portion of the second conductivelayer is located between the piezoelectric body and the substrate in thesecond direction.
 18. The piezoelectric actuator according to claim 17;wherein the first conductive layer is positioned between the portion ofthe second conductive layer and the piezoelectric body in the seconddirection.